Should SLS be cancelled, there will be 16 or so RS25D's available. If not, the production of these engines may be restarted.

I would propose the following:Close out the Delta 4 but use the 5 meter tooling to build a new Hydrolox booster.

Delta 5.Build a manrated 5 meter Delta 5 using two RS-25's and three Blue Origin BE-3's for the re-usable first stage. Since the BE-3's are restartable, use them for the boostback/reentry and landing burns. Second stage would be powered by one BE-3 vacuum optimized engine.Once this booster is in service, end production of the Atlas 5 and move the CST-100 to the new vehicle.A totally US built vehicle lifting a US built capsule.

Should SLS be cancelled, there will be 16 or so RS25D's available. If not, the production of these engines may be restarted.

I would propose the following:Close out the Delta 4 but use the 5 meter tooling to build a new Hydrolox booster.

ULA knows what their options are, and Vulcan is the plan. Plus, the RS-25 is NASA's problem, not ULA's, and it makes no sense for ULA to commit to spending their own money to bail out NASA. That makes no sense at all.

I came up with a similar, 'Rocket Lego' idea in an old thread. If SLS is cancelled but they (NASA, ULA etc) wanted to use the RS-25s up: use the Delta IV corestage powered by a single RS-25 and using 6x or 8x GEM-60 solid strap on boosters - aluminum/lithium structures would also help. The upper stage would be a single engine 5-meter Delta version with an upgrade path to an MB-60 as a more powerful upper stage. With the Delta IV corestage using the more efficient RS-25 as a sustainer engine; this would be a long burner, helping to keep the upper stage fat with propellants for a higher altitude. The increased number of GEM-60 solids on the corestage would compensate somewhat for the lower thrust of the RS-25 over the RS-68.

I wonder what someone like Steve Pietrobon or Ed Kyle could make of the performance figures for such a launcher?

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Replacing one RS-68 with two RS-25s (plus BE-3s) makes reuse economically mandatory from day one. The RS-25D wasn't exactly easy or cheap to reuse, and the RS-25E wasn't designed to be reusable at all. RS-25 wasn't the solution to economical RLV in the last century, and I can't imagine it's the solution to economical RLV in this century.

Vulcan is a more sensible plan for the Delta 4 tooling, in my opinion. I have trouble seeing how a semi-reusable-at-best Vulcan will compete with New Glenn or SpaceX, but with the engines available to ULA? It's either Vulcan, or a bunch of BE-3s (Delta 11?), or scale up to larger tooling and copy New Glenn.

Replacing one RS-68 with two RS-25s (plus BE-3s) makes reuse economically mandatory from day one. The RS-25D wasn't exactly easy or cheap to reuse, and the RS-25E wasn't designed to be reusable at all. RS-25 wasn't the solution to economical RLV in the last century, and I can't imagine it's the solution to economical RLV in this century.

Vulcan is a more sensible plan for the Delta 4 tooling, in my opinion. I have trouble seeing how a semi-reusable-at-best Vulcan will compete with New Glenn or SpaceX, but with the engines available to ULA? It's either Vulcan, or a bunch of BE-3s (Delta 11?), or scale up to larger tooling and copy New Glenn.

I understood that the last version flown of the RS-25 was good for up to 60 reflights (of shuttle duration or 8.5 minutes) without major overhaul. If that is the case even at 24 million a piece and assuming start/stop is the limiting factor you are talking only 0.8 million in engine cost per flight for Delta5. Say 1.5 million including inspection of all 5 engines.

And you get a man-rated booster, with a big enough 2nd stage to allow consideration of refueling in orbit.

Not everything deserves to be flown. Outside of the common avionics/tanks/stage fabrication/thrust structure, all of which are refined and used on Vulcan, can't think of anything worth reusing.

The plumbing can never be cheap enough. Neither RS-68 nor SSME would be optimal for booster engines. Integration is too difficult, the GSE/pad horrendously expensive to maintain.

If you were to compare flight systems between Atlas V and Delta IV, you'd find Delta shortcomings that Atlas better addresses.

As to US, Centaur delivers most of the performance over the larger DCSS for a fraction of the weight.

So apart from space cadet need to keep flying everything that can fly, can't think of the reason for anything more.

DIVH addresses a narrow need, likely to be surpassed soon. After that, there's just certain legacy need. Which will fade fast.

Delta IV was done in the shadow of the Shuttle, with the understanding that hydrolox was the ideal LRE, and the only better thing would be nuclear. As Tom Mueller/SX has found out, when you do the trades that doesn't always pan out.

Ariane 6 is the next hydrolox LV. Unlike Delta IV (but like Ariane 5), which can launch a useful payload w/o SRMs. Learning from its design, its more of a cost reduced version of its predecessor, including a different way to integrate the vehicle for flight with completely different pad/operations.

So if you were to follow the same formula, a Delta V would have a cost reduced but higher performance engine (how you'd do that might be a tap-off or double expander), fully integrate the vehicle horizontally, have a clean pad with a TE, and a mobile service structure that vertically integrates the vehicle with payload.

(Likely for competitive reasons, you'd desire a carbon fiber tanks/structures, and horizontal payload integration. If you were to reuse the booster, you'd want to have the engine throttle down like NS and land similarly downrange.)

Might you be able to do this - perhaps. It likely would cost a few billion. But what would you gain?

I came up with a similar, 'Rocket Lego' idea in an old thread. If SLS is cancelled but they (NASA, ULA etc) wanted to use the RS-25s up: use the Delta IV corestage powered by a single RS-25 and using 6x or 8x GEM-60 solid strap on boosters - aluminum/lithium structures would also help. The upper stage would be a single engine 5-meter Delta version with an upgrade path to an MB-60 as a more powerful upper stage. With the Delta IV corestage using the more efficient RS-25 as a sustainer engine; this would be a long burner, helping to keep the upper stage fat with propellants for a higher altitude. The increased number of GEM-60 solids on the corestage would compensate somewhat for the lower thrust of the RS-25 over the RS-68.

I wonder what someone like Steve Pietrobon or Ed Kyle could make of the performance figures for such a launcher?

Here's how I did this: I put in the numbers regarding the mass of each stage, typed in the altitude and inclination, calculated the payload weight, and subtracted that total by the mass of the payload attach fitting to get the actual payload weight.

The following performance numbers assume that this launch vehicle is situated at either SLC-37B in Cape Canaveral or SLC-6 in Vandenberg.

For the Delta V with 6 SRBs, GTO (185 by 35,786 at 27 degrees) payload is about 8566 kilograms, LEO (200 by 200 at 28.7 degrees) payload is about 24,581 kilograms, and SSO (600 by 600 at 98 degrees, or 800 by 800 at 98 degrees) payload is between 16,070 and 17,887 kilograms.

For the Delta V with 8 SRBs, GTO (185 by 35,786 at 27 degrees) payload is about 9632 kilograms, LEO (200 by 200 at 28.7 degrees) payload is about 27,099 kilograms, and SSO (600 by 600 at 98 degrees, or 800 by 800 at 98 degrees) payload is between 17,794 and 19,778 kilograms.

Here's how I did this: I put in the numbers regarding the mass of each stage, typed in the altitude and inclination, calculated the payload weight, and subtracted that total by the mass of the payload attach fitting to get the actual payload weight.

The following performance numbers assume that this launch vehicle is situated at either SLC-37B in Cape Canaveral or SLC-6 in Vandenberg.

For the Delta V with 6 SRBs, GTO (185 by 35,786 at 27 degrees) payload is about 8566 kilograms, LEO (200 by 200 at 28.7 degrees) payload is about 24,581 kilograms, and SSO (600 by 600 at 98 degrees, or 800 by 800 at 98 degrees) payload is between 16,070 and 17,887 kilograms.

For the Delta V with 8 SRBs, GTO (185 by 35,786 at 27 degrees) payload is about 9632 kilograms, LEO (200 by 200 at 28.7 degrees) payload is about 27,099 kilograms, and SSO (600 by 600 at 98 degrees, or 800 by 800 at 98 degrees) payload is between 17,794 and 19,778 kilograms.

I came up with a similar, 'Rocket Lego' idea in an old thread. If SLS is cancelled but they (NASA, ULA etc) wanted to use the RS-25s up: use the Delta IV corestage powered by a single RS-25 and using 6x or 8x GEM-60 solid strap on boosters - aluminum/lithium structures would also help. The upper stage would be a single engine 5-meter Delta version with an upgrade path to an MB-60 as a more powerful upper stage. With the Delta IV corestage using the more efficient RS-25 as a sustainer engine; this would be a long burner, helping to keep the upper stage fat with propellants for a higher altitude. The increased number of GEM-60 solids on the corestage would compensate somewhat for the lower thrust of the RS-25 over the RS-68.

I wonder what someone like Steve Pietrobon or Ed Kyle could make of the performance figures for such a launcher?

Here's how I did this: I put in the numbers regarding the mass of each stage, typed in the altitude and inclination, calculated the payload weight, and subtracted that total by the mass of the payload attach fitting to get the actual payload weight.

The following performance numbers assume that this launch vehicle is situated at either SLC-37B in Cape Canaveral or SLC-6 in Vandenberg.

For the Delta V with 6 SRBs, GTO (185 by 35,786 at 27 degrees) payload is about 8566 kilograms, LEO (200 by 200 at 28.7 degrees) payload is about 24,581 kilograms, and SSO (600 by 600 at 98 degrees, or 800 by 800 at 98 degrees) payload is between 16,070 and 17,887 kilograms.

For the Delta V with 8 SRBs, GTO (185 by 35,786 at 27 degrees) payload is about 9632 kilograms, LEO (200 by 200 at 28.7 degrees) payload is about 27,099 kilograms, and SSO (600 by 600 at 98 degrees, or 800 by 800 at 98 degrees) payload is between 17,794 and 19,778 kilograms.

The dry masses of the CBC and DCSS are different because I subtracted the mass of the RS-68 and RL-10 by the dry mass of each stage respectively and to each of those numbers, I added the mass of the RS-25D and MB-60 engines.

I apologize if this does not make sense, but I did try my hardest to explain everything, envy887.

A straight up re-engined first stage with two RS-25 engines bumps GTO payload up from 4.2 tonnes (RS-68A) to 6.5 tonnes (GEO - 1800 m/s). You could also stretch the first stage a bit, thanks to the higher thrust compared to a single RS-68A, and get 7.5 tonnes to GTO. A nice improvement, but at great cost.

The dry masses of the CBC and DCSS are different because I subtracted the mass of the RS-68 and RL-10 by the dry mass of each stage respectively and to each of those numbers, I added the mass of the RS-25D and MB-60 engines.

I apologize if this does not make sense, but I did try my hardest to explain everything, envy887.

No, that makes perfect sense. But check your ISP values. I've found that tool only gives realistic outputs when using the AVERAGE ISP, not the vacuum ISP (despite what the hover hint says). So the GEMs should be around 250, the SSME around 415, and the MB-60 467 seconds.

@ robert_dWe already have the Atlas V and the Falcon 9.Atlas V and Delta IV are expected to be replaced by Vulcan.We expect to have Falcon heavy and New Glenn.

It would be better to spend the time working on payloads and BLEO missions for these launchers.So why keep trying to find a replacement for SLS and or reuse of shuttle hardware? Very true SLS has to go sooner than later. It is holding the U.S. space program back by funding and resources.

Please forgive me, envy887. I made a typo when inputting the ISP for MB-60. It should have been 466.7 and not 266.9.

When you said, "use the AVERAGE specific impulse," are you referring to the specific impulse at sea level?

No, I mean the average specific impulse over the entire burn. A SL engine's specific impulse continuously increases from liftoff to burnout, while a vacuum engine operates at near constant specific impulse.

To get the exact average you need to integrate the Isp vs time curve for a specific launch profile and divide by duration, but for these purposes a simple average of SL and Vac Isp is typically close enough. For an SSME the average is around 410 to 415 seconds. For a SRB more like 250 seconds.

Their thrust-to-weight ratio is pretty terrible (sea level, 418klbf/7.7klb=54), so using them on a reusable rocket might be a fatal flaw. Of course, if you add 6-8 solids -- there went reusability -- you can drag an under-powered hydrolox core stage to orbit.

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One of my recent pet projects was reshuffling the Delta tanks for Methalox and sticking BE-4s on it. Does not really work out on the silverbird calculator though.I would love a tool where it is easier to change existing vehicles, without finding parameters and then retyping everything. Bonus points for an ensemble of results based on a parameter change.

If anything the RS-25 should be turned into a reusable second stage engine (~470s ISP) on top of a BE-4 booster.

The SSME was the original engine for the Ares-I upper stage but it needed to be restartable, which proved to be far to expensive to do. It is designed from the beginning to require ground based equipment to start. As for being reusable, that is not physically possible in the sense you are talking. That needs to be part of the fundamental base design.

« Last Edit: 05/26/2017 08:26 PM by clongton »

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If anything the RS-25 should be turned into a reusable second stage engine (~470s ISP) on top of a BE-4 booster.

The SSME was the original engine for the Ares-I upper stage but it needed to be restartable, which proved to be far to expensive to do. It is designed from the beginning to require ground based equipment to start. As for being reusable, that is not physically possible. That needs to be part of the fundamental base design.

I know people are huge fans of the SSME, but it is by now a pretty ancient design compared to newer engines. It is very expensive. And despite its great efficiency, it is not well suited for a reusable vehicle. Newer engines that are built with reusability in mind - M1D, BE-4, Raptor - are better choices for new rocket stages. Can't we just let the RS-25 retire with honor instead of trying to use it where it doesn't make sense?

If anything the RS-25 should be turned into a reusable second stage engine (~470s ISP) on top of a BE-4 booster.

The SSME was the original engine for the Ares-I upper stage but it needed to be restartable, which proved to be far to expensive to do. It is designed from the beginning to require ground based equipment to start. As for being reusable, that is not physically possible. That needs to be part of the fundamental base design.

I know people are huge fans of the SSME, but it is by now a pretty ancient design compared to newer engines. It is very expensive.

Boy and howdy!

It's a wonderfully compact ground start engine, perfect for a spaceplane! If you wanted to do a 1/3 scale carbon composite Shuttle variant, it would be the perfect technology base to start from.

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And despite its great efficiency, it is not well suited for a reusable vehicle.

Stage you mean. As in powered landing meaning restart. Agreed. Would work great for reuse on a flyback where you don't restart.

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Newer engines that are built with reusability in mind - M1D, BE-4, Raptor - are better choices for new rocket stages. Can't we just let the RS-25 retire with honor instead of trying to use it where it doesn't make sense?

Agree with the highlight I've done.

FWIW, the only way I could see RS-25E derivative used would be with either an air launched/started or ground launched/started (with side boost) spaceplane concept (unlike Shuttle by having integral LH/LOX tanks).

add:For a rapid deploy & recovery spaceplane single engine use *only*, there are some redesign/additive mfr/materials changes that could exploit hydrolox propulsion as originally intended for a vehicle in the capability class of the HL20. You could push it then well beyond the 108% thrust level.

The only advantage for such a vehicle might be a more rapidly reusable crew transport to LEO turnaround than Dreamchaser/Dragon/Starliner/derivative NS capsule.

I changed my mind. After re-reading the information available, I have come to believe that the RS-25D is just too complicated and thus too expensive. If it should turn out that they can simplify the design in the quest to make an expendable version, then find out it could still be reusable, I could reconsider.

So in the meantime, a simpler alternative: Add four BE-3's to the current Delta 4. The design already accepts solids, so it should be almost trivial (not really) to add plumbing. Use them for the boostback, ect. The landing legs should not be a challenge either. A few years ago, I remember reading they had run the RS-68 for as long as 700 seconds, so its quite possible that 3 flights per engine could happen now.

Then upgrade the engine to RS-68B with a regenerative bell and make it manrated.That should be a cheaper path to keeping a hydrolox booster in production.

I changed my mind. After re-reading the information available, I have come to believe that the RS-25D is just too complicated and thus too expensive. If it should turn out that they can simplify the design in the quest to make an expendable version, then find out it could still be reusable, I could reconsider.

So in the meantime, a simpler alternative: Add four BE-3's to the current Delta 4. The design already accepts solids, so it should be almost trivial (not really) to add plumbing. Use them for the boostback, ect. The landing legs should not be a challenge either. A few years ago, I remember reading they had run the RS-68 for as long as 700 seconds, so its quite possible that 3 flights per engine could happen now.

Then upgrade the engine to RS-68B with a regenerative bell and make it manrated.That should be a cheaper path to keeping a hydrolox booster in production.

RS-68 is still very expensive. And not reusable. Just because they ran one engine for 700s does not mean that this provides enough margin if it is used again. The ablative liner(s) in the nozzle would have to be refurbished for every flight. It would seem like perhaps 7-9 BE-3's would be an option if you wanted a reusable stage.

Can't we just let the RS-25 retire with honor instead of trying to use it where it doesn't make sense?

Only when NASA does...

LOL...sorry, I kid, I kid...just couldn't help it.

But question. Is there ever a good reason to do hydrolox for the first stage? And what I mean is that it seems kerolox is both cheaper (hardware and GSE requirements....hydrogen always seemed to have more requirements/issues for handling, loading, storage, etc...) and better performance pound per pound for a first stage booster. (we will see about methane...should be...but no hard numbers yet that I know of) Also, hydrolox first stages always seems to need solids to actually get going (has there ever been a Delta IV without solids attached?)

I guess I am just wondering, if thinking reusable and/or cheap, that hydrolox would ever be a good first stage booster? All of it's glory seems to be in the void of space where it shines supreme on the performance meter.

Sadly, the RS-25 will never again be used on a reusable spacecraft. It almost makes more sense to upgrade the RS-68 to a regenerative nozzle and more thrust. Combining that type of engine with a big cluster of GEM solids and a good upper stage would make for a formidable expendable launcher!

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Sadly, the RS-25 will never again be used on a reusable spacecraft. It almost makes more sense to upgrade the RS-68 to a regenerative nozzle and more thrust. Combining that type of engine with a big cluster of GEM solids and a good upper stage would make for a formidable expendable launcher!

Yah it's kinda a shame as the RS-25 is up to the task of powering a SSTO.A simplified RS-68 with a regen nozzle might be a lot cheaper.Ironically the Ares V design probably would be workable with regen RS-68s.

I changed my mind. After re-reading the information available, I have come to believe that the RS-25D is just too complicated and thus too expensive. If it should turn out that they can simplify the design in the quest to make an expendable version, then find out it could still be reusable, I could reconsider.

So in the meantime, a simpler alternative: Add four BE-3's to the current Delta 4. The design already accepts solids, so it should be almost trivial (not really) to add plumbing. Use them for the boostback, ect. The landing legs should not be a challenge either. A few years ago, I remember reading they had run the RS-68 for as long as 700 seconds, so its quite possible that 3 flights per engine could happen now.

Then upgrade the engine to RS-68B with a regenerative bell and make it manrated.That should be a cheaper path to keeping a hydrolox booster in production.

Why keep a hydrolox 1st stage?Why keep Delta IV with modifications? Just how long would it take to get to first launch if this concept were possible?

ULA is going with Vulcan with ACES ( with tanker and in-space refueling ).Blue Origin is going with New Glenn ( 2 and 3 stage version ).These should have no problem being cheaper than any Delta IV with greater payload mass to orbit.They will both be using the same 1st stage engine.

Sadly, the RS-25 will never again be used on a reusable spacecraft. It almost makes more sense to upgrade the RS-68 to a regenerative nozzle and more thrust. Combining that type of engine with a big cluster of GEM solids and a good upper stage would make for a formidable expendable launcher!

But not any cheaper than the Delta IV (which is VERY expensive), so I'm not sure I understand the point?

I changed my mind. After re-reading the information available, I have come to believe that the RS-25D is just too complicated and thus too expensive. If it should turn out that they can simplify the design in the quest to make an expendable version, then find out it could still be reusable, I could reconsider.

RS-25E is the expendable version that is being developed right now for SLS. I'm not sure how reusable this engine is though.

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Sadly, the RS-25 will never again be used on a reusable spacecraft. It almost makes more sense to upgrade the RS-68 to a regenerative nozzle and more thrust. Combining that type of engine with a big cluster of GEM solids and a good upper stage would make for a formidable expendable launcher!

But not any cheaper than the Delta IV (which is VERY expensive), so I'm not sure I understand the point?

It was once suggested to me that it would be cheaper to upgrade and modify an in use and in production engine like the RS-68 than to modify and 'bring back from the dead' the RS-25, which is itself from a class of vehicle that is now a half-decade into museum life...

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In hindsight I'd skip the "fast and cheap" RS-68 for a reworked RS-25. Switch to fabrication methods available in the 90s, integrate the improvements that were been developed at the time. Continue to improve over time.

I changed my mind. After re-reading the information available, I have come to believe that the RS-25D is just too complicated and thus too expensive. If it should turn out that they can simplify the design in the quest to make an expendable version, then find out it could still be reusable, I could reconsider.

RS-25E is the expendable version that is being developed right now for SLS. I'm not sure how reusable this engine is though.

I figure the RS-25E should still be reusable since the main change is a switch to a lower cost but heavier channel wall construction.

Though the RL-10 was reused on the DC-X and they looked at reusing the H-1 on the Saturn I.

In hindsight I'd skip the "fast and cheap" RS-68 for a reworked RS-25. Switch to fabrication methods available in the 90s, integrate the improvements that were been developed at the time. Continue to improve over time.

Can't be much more expensive at the end of the day.

How about designing and building a new engine?

And switch to fabrication methods from THIS century. (The 1990s are 20 years dead and gone.)

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RS-25E is the expendable version that is being developed right now for SLS. I'm not sure how reusable this engine is though.

My understanding is that they did not go with a full RS-25E development program. Instead, they are building more RS-25D engines with some incremental changes to reduce production cost.

- Ed Kyle

If I were of a cynical nature I would think this is excellent news. They've retained most of the performance and re-usability of the RS25 but with copies less than 30 years old (keeping in mind the issues when Orbital starting using refurbed NK33's on Antares).

That means a superb RLV engine will be available after the SLS is finally cancelled. IMHO SSME was the jewel in the crown of the STS programme. Unlike every other LRE (prior to SX and Blue's entry into the market) it was designed for reuse and had NASA implemented all the upgrades developed for it over the years (and a few obvious additions) it would have had a better T/W ratio while retaining the Isp (in fact perhaps with a bit better nozzle shape it might have even increased that).

But to the OP.

There will be a new Delta IV and Delta IV Heavy replacement.

It will be called Vulcan/ACES. I'd say that's going to happen. Nothing short of having ULA shut down will stop Tory Bruno from pushing it forward.

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In hindsight I'd skip the "fast and cheap" RS-68 for a reworked RS-25. Switch to fabrication methods available in the 90s, integrate the improvements that were been developed at the time. Continue to improve over time.

Can't be much more expensive at the end of the day.

How about designing and building a new engine?

And switch to fabrication methods from THIS century. (The 1990s are 20 years dead and gone.)

My alternate history is skipping the RS68 in the 90s. Using production methods from 2010s to build an entirely different engine is a bit more complicated at that time.

Today I would do a new engine.That said buying a new engine in the US is something that needs a whole lot of thinking. Engine development does not have a stellar track record when it comes to questions like on time or on budget.History is littered with 90 and 95% completed projects. Once you add more qualifiers into the mix there are very few engines left. "Flown at least once" seems to be a great acid test.

If there will be a new engine one of the first questions must be: Why hydrolox in a first stage?Does not make much sense unless you do something like Ariane 5/6 and using solids does not really help in a reusable world.

The dry masses of the CBC and DCSS are different because I subtracted the mass of the RS-68 and RL-10 by the dry mass of each stage respectively and to each of those numbers, I added the mass of the RS-25D and MB-60 engines.

I apologize if this does not make sense, but I did try my hardest to explain everything, envy887.

Strap-on version of GEM-60 SRM is nearing completion on its final-ever production run and its production line will be handed over to the GEM-63XL team. GEM-40/GEM-46 lines were updated and are currently being used for the standard version of GEM-63.

...Today I would do a new engine.That said buying a new engine in the US is something that needs a whole lot of thinking. Engine development does not have a stellar track record when it comes to questions like on time or on budget.History is littered with 90 and 95% completed projects. Once you add more qualifiers into the mix there are very few engines left. "Flown at least once" seems to be a great acid test.

If there will be a new engine one of the first questions must be: Why hydrolox in a first stage?Does not make much sense unless you do something like Ariane 5/6 and using solids does not really help in a reusable world.

Exactly. Hydrolox first stage only makes sense if the boosters rapidly reuseable (e.g. liquid with flyback or barge landing) and the main stage goes all the way to orbit AND BACK.

I don't think there's any reasonable argument to be made that an expendable hydrolox main stage with solid boosters will be commercially competitive.

It's a wonderfully compact ground start engine, perfect for a spaceplane! If you wanted to do a 1/3 scale carbon composite Shuttle variant, it would be the perfect technology base to start from.

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And despite its great efficiency, it is not well suited for a reusable vehicle.

Stage you mean. As in powered landing meaning restart. Agreed. Would work great for reuse on a flyback where you don't restart.

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Newer engines that are built with reusability in mind - M1D, BE-4, Raptor - are better choices for new rocket stages. Can't we just let the RS-25 retire with honor instead of trying to use it where it doesn't make sense?

Agree with the highlight I've done.

FWIW, the only way I could see RS-25E derivative used would be with either an air launched/started or ground launched/started (with side boost) spaceplane concept (unlike Shuttle by having integral LH/LOX tanks).

add:For a rapid deploy & recovery spaceplane single engine use *only*, there are some redesign/additive mfr/materials changes that could exploit hydrolox propulsion as originally intended for a vehicle in the capability class of the HL20. You could push it then well beyond the 108% thrust level.

The only advantage for such a vehicle might be a more rapidly reusable crew transport to LEO turnaround than Dreamchaser/Dragon/Starliner/derivative NS capsule.

This observation suddenly looks a lot more prescient in light of the announcement of the XS-1 award; Boeing will be partnering with AJR and flying an SSME-legacy main engine designated the AR-22:

Aerojet Rocketdyne, a subsidiary of Aerojet Rocketdyne Holdings, Inc. (NYSE:AJRD), was selected to provide the main propulsion for the Boeing and the U.S. Defense Advanced Research Projects Agency (DARPA) reusable Experimental Spaceplane (XS-1). Aerojet Rocketdyne is a member of the Boeing team that recently announced an agreement to collaborate with DARPA to design, build and test a technology demonstrator for the agency's XS-1 program.

The reusable experimental spaceplane is designed to deliver small satellites into orbit with high launch responsiveness. The main propulsion is based on the legacy space shuttle main engines (SSME).

"As one of the world's most reliable rocket engines, the SSME is a smart choice to power the XS-1 launch vehicle," said Aerojet Rocketdyne CEO and President Eileen Drake. "This engine has a demonstrated track record of solid performance and proven reusability."

For the XS-1 program, Aerojet Rocketdyne is providing two engines with legacy shuttle flight experience to demonstrate reusability, a wide operating range and rapid turnarounds. These engines will be designated as AR-22 engines and will be assembled from parts that remained in both Aerojet Rocketdyne and NASA inventories from early versions of the SSME engines. Assembly and ground testing will take place at NASA's Stennis Space Center in Mississippi.http://spaceref.com/news/viewpr.html?pid=50920

The other engine Boeing was looking at was the BE-3. The now designated AR-22 was the only other plausible rapid reusable hydrolox engine available.

But the weight range of this vehicle to LEO puts it at the very low end (actually about half that of a DIV without solids) as a replacement and starts Boeing into a competition with a subsidiary that they 50% own.

If Boeing could scale this vehicle up into a larger Medium class vehicle by factor of 5. Then it could become that highly competitive LV to SpaceX and also if partnered with Dreamchaser could represent a very cheap personnel transport to LEO. Also a scale up by factor of 5 puts it into direct competition with Vulcan (and SpaceX for which it would be a peer in probably Price) for the the lower end payloads which actually outnumber the larger payloads.

Could Boeing if successful with this vehicle be contemplating selling their interest in ULA. This vehicle if successful could kill ULA unless ULA goes with creating a rapid reusable 1st stage vehicle.

XS-1 would not be competing with Delta IV. Delta IV is finished, at least as far as he -M LVs are concerned. Also, it is a different beast, for a different application.

Regarding the program itself, it is an X- program. This means experimental and a technology demonstrator. Whether Boeing will decide to move on with the concept (a la X-33/Venture Star) will depend on a lot of things. And one of those is the fact that by the time you add 2-3 more SSMEs and a significant upper stage, the cost balloons to a territory they might not be comfortable with (at least as far as the commercial market is concerned).

The other engine Boeing was looking at was the BE-3. The now designated AR-22 was the only other plausible rapid reusable hydrolox engine available.

But the weight range of this vehicle to LEO puts it at the very low end (actually about half that of a DIV without solids) as a replacement and starts Boeing into a competition with a subsidiary that they 50% own.

If Boeing could scale this vehicle up into a larger Medium class vehicle by factor of 5. Then it could become that highly competitive LV to SpaceX and also if partnered with Dreamchaser could represent a very cheap personnel transport to LEO. Also a scale up by factor of 5 puts it into direct competition with Vulcan (and SpaceX for which it would be a peer in probably Price) for the the lower end payloads which actually outnumber the larger payloads.

Could Boeing if successful with this vehicle be contemplating selling their interest in ULA. This vehicle if successful could kill ULA unless ULA goes with creating a rapid reusable 1st stage vehicle.

I'm surprised Boeing didn't ask Northrop to dust off the TR-106 or TR-107 since it's not trying to be a SSTO and doesn't need an engine with as high of an ISP as the SSME.

The latter plus an expendable upper stage would be a near F9 v1.0 class LV.

My "Lego Rocket" would be a Delta IV core with either an RS-25 or RS-68 main engine, 2 4 segment Space Shuttle SRB's, and a J-2X third stage (or ACES if that would be better). It would be for NSS and NASA use only.Possibility of being built? negative zero... 😆

What about 5-7 BE-3's on the Delta 5m core, with a BE-3 vacuum upper stage ACES? That would be an all hydrolox vehicle, 1st stage may be able to land.

Would need 6 or 7 BE-3 engines to match RS-68A liftoff thrust. Nothing is known about BE-3 specific impulse or dry mass outside the halls of Blue Origin to my knowledge. As a starting point, lets assume it could be configured to match RS-68A's ISP (360 sec SL/414 sec Vac). An RS-68A weighs ~6,600 kg, so each BE-3 would have to weigh less than 940 kg (if seven were used) to match current Delta 4 CBC performance. For comparison, Merlin 1D is believed to weigh 470 kg. The BE-3U would have a bigger challenge matching RL10B-2, since the latter engine has ISP = 465 sec and only weighs ~300 kg including nozzle extension.

The primary benefit to this approach would be cost, rather than performance, although some performance gain might be possible. Would seven BE-3 engines cost less than one RS-68A? Would one BE-3U cost less than one RL10? Would CBC stage recovery be possible? Etc.

Fun to consider, but won't happen. That said, it does make me wonder if a BE-3 boosted launch vehicle might be worth considering for small payload applications.

What about 5-7 BE-3's on the Delta 5m core, with a BE-3 vacuum upper stage ACES? That would be an all hydrolox vehicle, 1st stage may be able to land.

Would need 6 or 7 BE-3 engines to match RS-68A liftoff thrust. Nothing is known about BE-3 specific impulse or dry mass outside the halls of Blue Origin to my knowledge. As a starting point, lets assume it could be configured to match RS-68A's ISP (360 sec SL/414 sec Vac). An RS-68A weighs ~6,600 kg, so each BE-3 would have to weigh less than 940 kg (if seven were used) to match current Delta 4 CBC performance. For comparison, Merlin 1D is believed to weigh 470 kg. The BE-3U would have a bigger challenge matching RL10B-2, since the latter engine has ISP = 465 sec and only weighs ~300 kg including nozzle extension.

The primary benefit to this approach would be cost, rather than performance, although some performance gain might be possible. Would seven BE-3 engines cost less than one RS-68A? Would one BE-3U cost less than one RL10? Would CBC stage recovery be possible? Etc.

Fun to consider, but won't happen. That said, it does make me wonder if a BE-3 boosted launch vehicle might be worth considering for small payload applications.

- Ed Kyle

Bezos has speculated about using New Shepard as a "BE-3 boosted launch vehicle" "for small payload applications". Making a multi-engine version could make sense for medium payloads.

BE-3U would have the advantage (in a potentially reusable system) of having about 6x the thrust of RL-10, which allows a much larger upper stage with lower staging and easier recovery of the core.